INFLUENCE OF RESPIRATION ON HEART-RATE AND BLOOD-PRESSURE FLUCTUATIONS

The dynamics of the respiratory and cardiovascular systems were studied by continuously slowing respiration from 0.46 to 0.05 Hz. The time-frequency distribution and global spectral analysis were used to assess the R-R interval (R-R) and the systolic and diastolic blood pressure fluctuations in 16 healthy subjects. During rest, the nonrespiratory-to-respiratory frequency ratios were not affected by occasional slow breathing, whereas the low- (0.01-0.15 Hz) to high- (0.15-0.3 Hz) frequency indexes for blood pressure were increased (P < 0.05). The respiratory fluctuations in R-R and the systolic and diastolic pressures were paced over the 0.46- to 0.05-Hz range. As respiration slowed to 0.07-0.09 Hz, the frequency content of the respiration and cardiovascular variables increased sharply and nonlinearly to a maximum that exceeded values at higher frequencies (P < 0.001). The nonrespiratory frequency content remained stable in the 0.01- to 0.05-Hz range and did not significantly differ from that at rest. In contrast, the nonstable 0.05- to 0.1-Hz component was suppressed. A slow 0.012- to 0.017-Hz rhythm modulated respiration and hemodynamic fluctuations at both respiratory and nonrespiratory frequencies. The study indicated that respiration input should be considered in the interpretation of global spectra. Furthermore the time-frequency distributions demonstrated that a close nonlinear coupling exists between the respiratory and cardiovascular systems.